Acclimation of the cold-water coral Lophelia pertusa to predicted rises in atmospheric CO2 and sea temperature UK Ocean Acidification

Research Programme

Wicks LC1, Hennige SJ1, Roberts JM1,2, 3

Introduction

Methods

Results

Conclusions

Cold-water corals are amongst the most three-dimensionally complex deep-sea habitats known and are associated with high local biodiversity1. However, their remoteness and the relatively short history of ecological research in these habitats mean that to date, we have little information on how these ecosystems will fare in the face of predicted future climate change.

Projected rises in atmospheric pCO2 will reduce the oceanic pH and the availability of carbonate ions (ocean acidi�cation, or OA), and increased sea temperatures may perturb cold-water coral systems beyond their thermal limits.

Indeed, cold-water corals are likely to be among the �rst a�ected by ocean acidi�cation2 as they inhabit a large bathymetric range, and as such many lie close to the aragonite saturation horizon. With OA, the ASH is predicted to become shallower, making it more di�cult for calcifying organisms near this depth to maintain their calci�ed structures, and thus a�ecting net reef growth.

Currently, the single and synergistic e�ects of projected increases in atmospheric pCO2 and sea temperatures upon the cold-water coral Lophelia pertusa are unknown. Studies to date have only examined L. pertusa response to either increased temperature or increased CO2 on short time scales3,4. However, short-term studies may not re�ect L. pertusa acclimation to synergistic stressors.

Furthermore, studies to date have focused on growth rates and ranged from very short term (24 hours4) on freshly collected coral, to long-term (6 months5) experiments on laboratory-kept specimens. However, to fully understand how the impact of increased CO2 on CWC, it is important to combine growth rates with measures of metabolism.

In this study, we examined the short and long term e�ects of OA and warming on the calci�cation and metabolism of L. pertusa, to determine whether acclimation will occur in a future warmer, high CO2 world.

Ocean Acidi�cation

In the short term, there was a signi�cantly negative e�ect of OA on L. pertusa, however partial acclimation was apparent after three months with no sign�cant reduction in respiration. It may be that energetic reserves are being used to mitigate the reduced energy production by respiration observed in the short term, however this will not be sustainable in the long term.

Temperature

Although there was no signi�cant change in calci�cation and respiration in response to temperature, the results were highly variable. Further analysis will be possible after 6 and 12 month time points.

Combined e�ect (most likely scenario)

Despite a signi�cant reduction in respiration rate compared to controls after 3 months, acclimation appears to have occured after 6 months, when there is no sign�cant di�erence in calci�cation rates.

Our results suggest that L. pertusa has both shock and acclimation responses to OA and warming. Indeed, the two-week period observed here before any noticeable di�erences were observed between experimental and control fragments may indicate a switching of metabolic pathways cued by extended exposure to elevated CO2.

Although it appears acclimation may be possible in a future of warmer, high CO2 seas, L. pertusa will be reliant on a sustained or potentially enhanced energetic input, of which we know little. Indeed, if calci�cation is sustained but at a higher energetic cost, the reallocation of energy away from reproductive output and maintanance could have e�ects at the population level.

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1: Centre for Marine Biodiversity and Biotechnology, Heriot-Watt University, Edinburgh, EH14 4AS, UK 2: Center for Marine Science, University of North Carolina Wilmington, 601 S. College Road, Wilmington, NC 28403-5928, USA3: Scottish Association for Marine Science, Scottish Marine Institute, Oban, Argyll, PA37 IQA, UK

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Rep. of IrelandUnited

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Sea of the HebridesMingulay

7°30’0’’W 7°0’0’’W 6°30’0’’W

56°30’0’’N

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Sample collection

Colonies of L. pertusa were collected from the Mingulay Reef Complex, Area 1 (56° 49.38 N, 7° 22.56 W, Fig.1), during the Discovery D366/7 UK Ocean Acidi�cation Expedition in July 2011. Colonies were collected from 141 - 167 m using a modi�ed video assisted van-Veen grab. Upon return to the surface, corals were placed in a holding tank at ambient temperature for 2 days, to recover from collection. Corals were then carefully fragmented into smaller pieces for experiments.

Short term experiments

Coral fragments were subject to two CO2 levels for 21 days: 380 and 750 ppm. CO2 levels were achieved using pre-mixed gas bubbling into chilled tanks at ambient reef temperature. Corals were fed every 2 days. Physiological measurements were taken at time zero, and after 7, 14 and 21 days.

Long-term experiments

Upon return to HWU, coral fragments were distributed between 20 seperate OA mesocosms, with four mesocosms for each treatment. The treatments were: 9°C and 380 ppm, 9°C and 750 ppm, 9°C and 1000 ppm, 12°C and 380 ppm, 12°C and 750 ppm. Corals were fed 3 times per week. Physiological measurements were taken at time zero, and after 3, 6 and 12 months.

Physiological measurements

For both experiments, metabolic rates were determined in coral fragments placed within 220 mL incubation chambers �tted with oxygen optodes connected to a temperature-compensated oxygen analyser (Oxy-4 Mini with Temp-4, Presens & Loligo systems). Rates of calci�cation and growth were determined using the alkalinity anomaly technique6 (AAT) with 4 h incubations, and 14C and 45Ca for 6 h incubations. The buoyant weight technique7 was also used for the long term experiment.

Short term

L. pertusa respiration rate decreased in acidi�ed conditions (750ppm, 11.4 ± 1.39 SE, µmol O2 g-1 tissue dry weight h-1) over 21 days compared to present day conditions (28.6 ± 7.30 SE µmol O2 g-1 tissue dry weight h-1), with a signi�cant di�erence between treatments only being observed after 2 weeks. (Fig. 3).

L. pertusa calci�cation rate (AAT) did not change in control or acidi�ed conditions (750ppm) over 21 days (Fig. 4). Calci�cation rate as determined by 14C uptake also did not di�er between treatment and control fragments at either the experiment start or end (390 ppm; 1.68 x 10-2 (± SE 0.60), 750 ppm; 4.38 x 10-2 (± SE 1.6) µmol CaCO3 g-1 tissue dry weight h-1). However, there was a signi�cant decrease in calci�cation rates measured by 14C uptake in 380 ppm fragments over time, which was not signi�cant in 750 ppm fragments, due to very high variability.

Long term

After 3 months, respiration rate of L. pertusa was highest in the control treatment (9°C, 380 ppm, 3.5 ± 0.42 SE, µmol O2 g-1 tissue dry weight h-1), but was not signi�cantly di�erent from all single stressor treatments (enhanced CO2 treatments, or the increased temperature/ambient CO2 treatment, Fig. 5). The dual-stressor treatment of increased temperature and CO2 had signi�cantly lower respiration rates (1.5 ± 0.42 SE, µmol O2 g-1 tissue dry weight h-1) than all other treatments.

Growth was reduced after 3 months in the dual-stressor treatment (0.18% increase) compared to the ambient CO2 treatments (1.9-2.7%, Fig. 6). Indeed, all L. pertusa in enhanced CO2 treatments showed lower growth rates than corals in ambient CO2. However, after 6 months there was no sign�cant di�erence in growth between all treatments (2.2-3.2% increase).

All respiration measurements are presented normalised to tissue dry weight. It should be noted that respiration rates declined over time in all aquaria-kept corals, likely due to the feeding limitations of aquaria in comparison to the in situ food supply.

Fig. 1. Location of Mingulay Reef Complex with colour multibeam bathymetry. Sample area has been circled on the multibeam map.

Fig. 2. Lophelia pertusa in tanks, respiration chambers, and with polyps out. RRS Discovery at Mingulay.

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References: 1. Roberts et al. (2006) Science 312: 543-547; 2. Guinotte et al. (2006) Front Ecol Environ 4:141–146; 3. Dodds et al. (2007) MEPS 397:113-124; 4. Maier et al. (2009) Biogeosciences 6(8):1671-1680; 5. Form & Riebesell (2012) Glob Change Biol 18:843-853; 6. EPOCA Best Practices Guide (2011); 7. Davies (1989) 101:389-395

Acknowledgements: UK Ocean Acidi�cation Research Programme (Natural Environment Research Council grant NE/H017305/1) and the European Commission’s Seventh Framework Programme (FP7/2007-2013) project EPOCA (grant agreement n° 211384). Juan Moreno-Navas, Kim Last (SAMS), participants on Discovery Cruise D366/7, Solvin Zankl for images.